An electronic system to operate an electromechanical parking brake of a land vehicle is described, having an input unit to detect a driver request for parking brake, which request is evaluated by at least one control unit which controls at least one actuating unit for activating at least one brake.
DE 196 53 541 A1 discloses an electrically activatable actuating device for motor vehicle parking brakes. The actuating device comprises two electric motors which are controllable separately from one another for activating the brakes. Furthermore, the actuating device comprises a control unit for controlling the electric motors according to a driver request for braking. The two electric motors are contained in a common receiving housing and are axially displaceable in the housing in relation to the wheel axles of the motor vehicle. The motors act by means of a threaded spindle and a threaded nut on actuating elements of the brakes. One of the two electric motors is designed for regular activation of the brakes. The other of the two electric motors is activatable via an emergency switch for use in emergency operation. Activation of the parking brakes by one electric motor or the other is possible owing to the axial displaceability of the two electric motors relative to their receiving housing. The electric motor to be controlled in emergency operation is fed from a circuit which is independent of the power supply of the control unit and the electric motor for normal operation. Release and application of the brakes is thus possible even in the event of failure of one electric motor or one of the two power supplies.
An input unit to detect a driver request for parking brake for an electromechanical parking brake system is known from EP 1 128 999 B1. In this case, the input unit is in connection with an electronic control unit which for its part converts the signals, supplied from the input unit, directly into corresponding control signals for an actuating unit, in order to transform the parking brake system into the desired activation state. In order, even in the event of a fault, to enable detection of the driver request for parking brake with regard to an activation of the parking brake system, i.e. application or release, and at the same time a fault diagnosis, the input unit according to EP 1 128 999 B1 must be designed as a push-button or rocker switch with a plurality of switching positions and in each switching position supply at least two redundant signals to the electronic control unit.
A parking brake system for motor vehicles, having an operating element, two actuators with assigned control units and a redundant power supply, is known from DE 10 2007 029 632 A1, and corresponding US patent publication No. 2009/200124 A1, the US document being incorporated by reference herein. The parking brake system comprises four mutually independent signal lines for transmitting control signals, corresponding to a driver request, from the operating element to the actuators. A signal line is formed in each case between the operating element and the control unit of each actuator, between the two actuators themselves and directly between the operating element and the two actuators. Owing to this configuration, the parking brake system remains fully functional in the event of failure of individual components. Even in the event of a fault in one of the actuators, the other actuator remains fully functional independently thereof.
DE 197 51 431 A1 discloses an electromechanical parking brake system for motor vehicles, having a control device for controlling motor-activatable parking brakes and a redundant energy supply. For the redundant energy supply, the parking brake system has a reserve battery in addition to a main energy supply unit. The control device comprises a plurality of control units working in parallel for separate processing of input signals. Each of the control units is separately supplied with energy. Thus, it is still possible to activate one of the actuating motors for actuating at least one parking brake if an electrical fault occurs in one of the branches in the parking brake system.
A redundant energy supply of an electrical parking brake for motor vehicles is known from DE 197 58 289 A1. In the event of a main battery not being available, the electrical parking brake is fed by an auxiliary battery, the auxiliary battery being based on a technology different to the main battery and/or having a different loading profile to the main battery. For the switch-over process between the main and auxiliary battery, there is provided in the motor vehicle a switch-over means to uncouple the parking brake from the main battery and connect it to the auxiliary battery.
An electrical brake system, in which the energy supply of the elements contained in the brake system is effected by at least two independent on-board networks, is known from DE 196 34 567 A1, and corresponding U.S. Pat. No. 5,952,799 A, the US document being incorporated by reference herein. The brake system has control modules on the vehicle wheels for adjusting the braking force and a control module for detecting a driver request for braking. At least two independent information paths are provided between the modules, and at least one of the modules and one of the information paths are fed from a different on-board network to the other modules and information paths. In the event of a fault, control signals are supplied to the wheel control modules directly from a pedal unit which detects the driver request for braking, so that braking operation is ensured in one information path even in the event of a fault. The fault detection is effected by comparing signals supplied to the wheel control modules via the individual information paths. If the result of the comparison is inconsistent, a fault is present.